1. Technical Field
This invention relates to articles made of material compositions primarily composed of electrically non-conductive oxide silicon material in combination with fractions of materials that render the overall article electrically conductive.
2. Related Art
One important commercial application for such material compositions is thin film technology. Many architectural, automotive, integrated circuit, flat panel display and optical devices require thin films of oxide silicons (SiOx), such as silicon dioxide (SiO2).
One of the principal methods for producing such thin films is by a physical vapor deposition process known as radio frequency (RF) sputtering. This method utilizes non-conductive silicon dioxide material as the source material for the creation of the silicon dioxide thin film coatings. A high frequency ac-voltage, typically 13.56 MHz is applied capacitively to the target. In one phase, gas ions of the plasma are accelerated toward the target and cause material at the surface of the target to be detached as a result of the bombardment with the gas ions. In the other phase, the charge on the target surface is neutralized with the result that no sputtering occurs during this periodic phase. Although this method produces suitable silicon dioxide thin film coatings, it has the limitations of requiring the use of expensive and complex high frequency power supplies, low deposition rates for the formation of the SiO2 thin film coatings, and inherent limitations on the uniformity of SiO2 coatings that can be created with such method.
Direct current (DC), including pulsed DC, or medium to low frequency alternating current (AC) sputtering processes do not have such limitations. However, DC and AC processes require the use of silicon as the source material for the SiO2 coating. To utilize silicon as the deposition source material, it must be made sufficiently electrically conductive either by doping with a suitable dopant such as boron, or by the addition of small amounts of aluminum or other suitable metals. To use such silicon targets to create SiO2 thin films via DC or AC sputtering also requires that large amounts of oxygen be introduced into the sputtering process. The resultant process is referred to as reactive sputtering. The oxygen reacts with the silicon during the sputtering process to yield SiO2. To create SiO2 films typically requires that O2 gas pressure be 30- 50% of the total gas pressure in the vacuum chamber. This can result in a significant process mismatch in terms of the oxygen requirements, as compared to that required for other sputtered thin films which may be deposited using the same vacuum vessel. The presence of significant levels of O2 in the chamber further slows the rate of deposition through collisions with the sputtered material. In addition, SiO2 films made by DC and AC sputtering from silicon or Si:Al targets generally are not sufficiently dense and crystalline as a result of the characteristics of reactive deposition to render them suitable for many semi-conductor, flat panel and opto-electronics applications. The SiO2 film compositions produced by such reactive processes generally exhibit less useful optical, mechanical and chemical durability properties compared to those produced by RF sputtering of non-conductive SiO2 targets.